Cleaning sponge roller

ABSTRACT

A cleaning sponge roller is made of a polyvinyl acetal-based porous sponge having elasticity in a wet state and comprises a generally cylindrical roll body and a plurality of protrusions molded integrally on the periphery of the roll body. The cleaning sponge roller rotatingly cleans a material to be cleaned by contacting the top portions of the protrusions with the surface of the material and brushing off polishing residues found on the surface of the material. Each of the protrusions has a tapered protruding base portion extending from the periphery of the roll body, and a protruding end portion having almost the same sectional shape from the top end surface of the protruding base portion to the top portion.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.09/503,626, filed Feb. 11, 2000, now U.S. Pat. No. 6,502,273, which is acontinuation-in-part of application Ser. No. 09/297,617, filed Jun. 25,1999 which is now abandoned, which is a national stage ofPCT/JP97/03971, filed Oct. 31, 1997, which applications are herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a cleaning sponge roller forremoving fine particles such as abrasive grains, swarfs and scobs offthe surface of a material. More particularly, the present inventionrelates to a sponge roller for cleaning a material surface in theprocess of producing substrates such as magnetic recording aluminumdiscs, semiconductor silicon wafera, and the like. The present inventionalso relates to a mold for forming the sponge roller.

2. Description of Related Art

A process of producing a hard disc, a silicon wafer, or the like(including, but not limited to, a glass disc, a semiconductor elementwhich is subjected to a chemical mechanical polishing (CMP) work, aphotomask, a liquid glass substrate, etc.) requires a step of highprecision abrasion or “polishing,” which provides a surface of the diskor wafer with an extremely high precision finish. The high precisionfinish is achieved by polishing the surface with abrasive grains such assilicon oxide particles, alumina particles or cerium particles. Whenthis step is complete, however, the surface is contaminated with theresidue of the polishing, such as grains, swarfs and/or scobs. Theresidue must be cleaned before the material can undergo a subsequentstep.

Several conventional cleaning methods have been known. The RCA cleaningmethod, one of the conventional methods for cleaning silicon wafers,uses a mixture of aqueous ammonia and hydrogen peroxide and a mixture ofdilute hydrofluoric acid, hydrochloric acid and hydrogen peroxide.Another conventional method for cleaning a hard disc, silicon wafer,etc. is a method of using a cleaning sponge roller made of a polyvinylacetal-based (“PVAt-based”) porous material.

For example, as shown in FIG. 6, a sponge roller 51 is used to clean asurface 9 a of a material 9. The sponge roller 51 typically includes aroll body 3 having a peripheral area 3 a and a plurality of protrusions53 integrally protruding from the peripheral area 3 a. A top portion 53b of the protrusion 53 is brushed in a direction indicated by an arrowagainst the surface 9 a of the material 9 by pressing the protrusions 53onto the surface 9 a and subsequently separating the protrusions 53 fromthe surface 9 a. The pressing and separating motions are repeated. As aresult, the material 9 is brushed with the sponge.

As shown in FIG. 6, the protrusions 53 are generally columnar shaped,having almost the same cross-sectional shape from a base end surface 53a of the protrusion 53 to a top end surface 53 b. When such columnarshaped protrusions brush against the surface 9 a, a tension acting onthe protrusion 53 concentrates at the base end surface 53 a and causesthe base end surface 53 a to be locally deformed in its vicinity. Inaddition, since the peripheral area 3 a is not completely flat butinclines toward the opposite side of the protruding direction of theprotrusion 53 in a shape of a circular arc, it is not cleanly deformedin a lateral direction compared to a case wherein the protrusion isattached to a completely flat surface. Therefore, a front end portion 55connecting the base end surface 53 a with the periphery 3 a of the rollbody 3 becomes easily broken.

Such a problem can be solved by forming the protrusions in a larger sizeto enhance the strength thereof. However, this creates another set ofproblems in that a desired brushing effect is not obtained and thecleaning effect may be lowered.

SUMMARY OF THE INVENTION

It is an object of an embodiment of the present invention to provide aPVAt-based sponge roller with an improved durability without decreasingthe quality of cleaning performance.

To attain the object described above, in accordance with one embodimentof the present invention, a cleaning sponge roller has a generallycylindrical roll body and a plurality of protrusions molded integrallyon the periphery of the roll body. The periphery of the roll bodyrotates and brushes polishing residue off the material to be cleaned.Each of the protrusions of the roll body has a tapered protruding baseportion extending from the periphery of the roll body, and a protrudingend portion having generally the same sectional shape extending from thetop end of the protruding base portion to the top portion of theprotruding end portion. The protruding base portion may be formed in ashape of generally truncated corn. The protruding end portion may beformed in a generally columnar shape or a generally cylindrical shape.

With the above construction, the protruding base portion of theprotrusion has an outer surface formed in a divergent shape toward theperiphery of the roll body and a sectional area of the protruding baseportion attains a maximum at the base end (border between the peripheryof the roll body and the protruding base portion) and graduallydecreases toward the protruding end portion. Therefore, when each of theprotrusions is pressed in the lateral direction, a stress concentrationin the vicinity of the base end of the protruding base portion where thetension is concentrated is dispersed in the whole protruding baseportion. Thus, the protrusion according to the present invention issignificantly more durable than the protrusions of conventional spongerollers.

Since the durability of the protrusions can be improved without exertingany influence on the shape of the protruding end portion, the protrudingend portion that is to be contacted with the material to be cleaned canreadily be formed into a size and a shape that are most suitable forbrushing.

In accordance with one embodiment, a cleaning sponge roller is formedfrom a polyvinyl acetal-based porous sponge that is obtained by reactinga viscous mixed solution containing raw materials in a mold. The moldcorresponding to the sponge roller with the above construction comprisesa first space for forming a roll body and a plurality of second spacesfor forming protrusions. Each of the second spaces comprises a baseportion forming space for forming a protruding base portion and an endportion forming space for forming a protruding end portion. The baseportion forming space communicates with the first space on one side andthe end portion forming space on the other.

The base portion forming space has an inclined surface extending towardthe first space from the end portion forming space. In the production ofthe sponge roller, the mixed solution is poured into the first space andthen the solution flows into each second space from the first space. Inthis case, since the base portion forming space of the second space hasan inclined surface extending toward the first space, the mixed solutionflows smoothly into the end portion forming space guided by the inclinedsurface of the base portion forming space. At the same time, an air inthe second space moves smoothly to the first space from the end portionforming space and then is released in the air from the first space.Consequently, the mixed solution can be securely charged to the terminalend of the second space, thereby making it possible to reduce theproduction cost due to an improvement in yield.

The height from the periphery of the roll body to the top end of theprotruding base portion is preferably not more than one-half, and morepreferably not less than one-fifth times as long as that of theprotrusion.

When the height of the protruding end portion exceeds one-half times aslong as that of the whole protrusion, there is a possibility that thedeformation amount of the protruding end portion is reduced and thebrushing effect on cleaning becomes insufficient. On the other hand,when the height of the protruding end portion exceeds one-fifth times aslong as that of the whole protrusion, there is a possibility thatsufficient strength cannot be obtained.

The crossed axes angle between a straight line, which connects the baseend and top end of the outer surface of the protruding base portion, andthe periphery of said roll body in an arbitrary section is preferablyfrom 30° to 60°.

When the crossed axes angle is smaller than 30°, there is a possibilitythat the protruding base portion may extend largely toward the peripheryand an area of the lower end surface of the protruding end portion mayincrease, thereby limiting the total number of the protrusions which maybe formed on the periphery of the roll body. On the other hand, when thecrossed axes angle exceeds 60°, there is a possibility that sufficientstrength may not be obtained.

Furthermore, the shape of the outer surface of the protruding baseportion may also be a linear inclined surface or a curved inclinedsurface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a partially cut perspective view of a cleaning spongeroller according to a first embodiment of the present invention.

FIG. 1(b) is an enlarged perspective view of a protrusion of the spongeroller shown in FIG. 1(a).

FIG. 1(c) is a sectional view of the protrusion of the sponge rollershown in FIG. 1(b).

FIG. 2 is a partially cut perspective view of a mold for molding thesponge roller shown in FIG. 1(a).

FIG. 3 is a sectional view showing a process for producing the spongeroller shown in FIG. 1(a).

FIG. 4 is a side view schematically showing the operation of the spongeroller shown in FIG. 1(a).

FIG. 5 is an enlarged view showing operation of the principal portion ofthe sponge roller of FIG. 4.

FIG. 6 is an enlarged view showing the operation of the principalportion of a conventional sponge roller.

FIG. 7 is a sectional view showing a protrusion of the sponge rolleraccording to a second embodiment of the present invention.

FIG. 8 is a graph showing the results of comparison tests of the tensilestrengths between a sponge roller having conventional type protrusionsand the sponge roller having the type of protrusions according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1(a) is a partially cut perspective view of a cleaning spongeroller 1 according to a first embodiment of the present invention. Thecleaning sponge roller 1 is made of a polyvinyl acetal-based porousmaterial (PVAt-based porous material) which is elastic in a wet statebut cured in a dry state. The PVAt-based porous material has excellentwater absorption properties and water retention properties and presentspreferable flexibility, suitable impact resilience, and good wearresistance.

The sponge roller 1 comprises a generally cylindrical roll body 3 and aplurality of protrusions 5 molded integrally on the periphery 3 a of theroll body 3.

FIG. 1(b) and FIG. 1(c) illustrate an enlarged view of the protrusion 5of the sponge roller 1 shown in FIG. 1(a). The protrusion 5 comprises aprotruding base portion 11 protruding integrally from the periphery 3 aof the roll body 3, and a protruding end portion 13 extending integrallyfrom a top end surface 11 b of the protruding base portion 11. A baseend surface 11 a of the protruding base portion 11 is included in theperiphery 3 a of the roll body 3. The top end surface 11 b of theprotruding base portion 11 and the base surface 13 a of the protrudingend portion 13 are the same.

The protruding base portion 11 is formed in a shape of a generallytruncated cone which is tapered toward the top end surface 11 b from thebase end surface 11 a. The protruding base portion 11 has an inclinedsurface 15 connecting the base end surface 11 a and the top end surface11 b of the protruding base portion 11; the base end surface 11 aconnects the inclined surface 15 at a base end 15 a, while the top endsurface 11 b connects the inclined surface 15 at a top end 15 b. Theinclined surface 15 is formed linearly and divergently from the top end15 a toward the bottom end 15 b.

The protruding end portion 13 extends in a direction almostperpendicular to the periphery 3 a of the roll body 3, and is formed ontop of the top end surface 11 b of the protruding base portion 11. Theprotruding end portion 13 has a generally cylindrical shape havingalmost the same cross-sectional shape from the base end surface 13 a tothe top end surface 13 b. The top end surface 13 b of the protruding endportion 13 approximately perpendicularly connects the periphery of theprotruding end portion 13.

The protruding base portion 11 has a height h, which represents thedistance measured along a line perpendicular to the periphery 3 a fromthe base end surface 11 a to the top end surface 11 b. The protrusion 5has a height H, which represents the distance also measured along theline perpendicular to the periphery 3 a from the periphery 3 a of theroller body 3 to the top end surface 13 b of the protruding end portion13 which also constitutes a top end surface of the protrusion 5. Theheight h of the protruding base portion 11 is set within an approximaterange of one-fifth to one-half of the height H of the protrusion 5. Astraight line 17 on the inclined surface 15, represents the shortestdistance between the base end 15 a and the top end 15 b of the inclinedsurface 15. The straight line 17 intersects with the periphery 3 a ofthe roll body 3 at angle θ₁ ranging from 30° to 60°.

The cleaning sponge roller 3 is obtained, for example, by mixing one ormore polyvinyl alcohols (raw materials) having a mean polymerizationdegree of 300 to 2000 and a saponification degree of not less than 80%to form an aqueous solution; adding aldehydes as cross-linking agents,minerals as catalysts and a starch as a pore-forming agent to theaqueous solution; pouring a mixed solution thereof into a mold 21 asshown in FIG. 2; reacting the mixed solution at 50-80° C.; taking outthe reaction product from the mold 21; and washing it with water toremove the pore-forming agent.

The mold 21 comprises an outer mold 23, an inner mold 25, a bottom plate27, a mandrel 29 and a cap 31. Both of the outer mold 23 and inner mold25 are formed in a cylindrical shape. The inner mold 25 has an outerdiameter, which is the same as or slightly smaller than an innerdiameter of the outer mold 23, and is inserted into the outer mold 23.The mandrel 29 is inserted into almost the center of the inner mold 25.The bottom plate 27 serves to cover lower ends 23 a and 25 a of theouter mold 23 and inner mold 25, respectively, and to support a lowerend 29 a of the mandrel 29. The cap 31 is fit within an upper end 23 bof the outer mold 23. The mandrel 29 is positioned by the bottom plate27 and cap 31.

As shown in FIG. 3, a generally cylindrical first space 33 for formingthe roll body 3 is partitioned between the inside of the inner mold 25and the periphery of the mandrel 29. The inner mold 25 is provided witha plurality of through holes (second spaces) 35 for forming theprotrusion 5. Each of the through holes 35 comprises a base portionforming space 37 for forming the protruding base portion 11 and an endportion forming space 39 for forming the protruding end portion 13. Thebase portion forming space 37 is connected to the first space 33 and theend portion forming space 39 is connected to the base portion formingspace 37. The base portion forming space 37 has an inclined surface 41extending toward the first space 33 from the end portion forming space39.

The mixed solution is poured into the first space 33 through a castingnozzle 43 inserted between the outer mold 23 and the cap 31, and thenthe solution flows into each of the through holes 35 from the firstspace 33. In this case, the mixed solution flows smoothly into the endportion forming space 39 guided by the inclined surface 41 extendingtoward the first space 33. At the same time, an air in the through hole35 moves smoothly from the end portion forming space 39 to the firstspace 33 and then is released in the air. Consequently, the mixedsolution can securely fill up to the terminal end of the through hole 35(end portion forming space 39). Accordingly, the yield is improved andthe production cost is reduced.

For a PVAt-based porous material, a material having a 30% compressionstress in a proper water-containing state of 15 to 150 g/cm² ispreferred. The “proper water-containing state” refers to awater-containing state where the PVAt-based porous material can exhibitproper plasticity, and the water content (weight percentage in thewater-containing state based on the dry state) is within a range fromabout 100% to 1000%. The “30% compression stress” refers to a valueobtained by cutting the PVAt-based porous material in a properwater-containing state so that a distance between both end surfaces(height in the longitudinal direction) becomes 30 mm, mounting the cutsample in a digital load measuring apparatus so that a load is appliedto the whole end surface, compressing in the longitudinal direction by30% (9 mm), measuring the load at which the cut sample was broken, anddividing the load by an area of the end surface.

The upper limit of the preferred range of 30% compression stress in theproper water-containing state is set at 150 g/cm² because a PVAt-basedporous material having a higher water-containing state than 150 g/cm²does not exhibit elasticity required for brushing. Similarly, the lowerlimit of the preferred range of the 30% compression stress in the properwater-containing state is set to 15 g/cm² because a PVAt-based porousmaterial having a lower water-containing state than 15 g/cm² is too softand causes distortion when the roll body 3 is rotated.

For a PVAt-based porous material, a material having a porosity of 85% to95% and an average pore diameter of 10 gm to 200 gm is preferred. Whenthe porosity is smaller than 85%, the flexibility in a wet state becomesinsufficient. Similarly, when the porosity is larger than 95%, nomaterial is suited for cleaning because of an insufficient practicalstrength. When an average pore diameter is smaller than 10 gm, asufficient brushing effect cannot be obtained because of insufficientelasticity in a wet state. Similarly, when an average pore diameterexceeds 200 gm, the material is not suited for cleaning because of anexcessive coarse pitch between the pores.

The “porosity” according to the embodiment is obtained by measuring witha dry automatic densimeter an apparent volume and a true volume of aPVAt-based porous material having a shape of a rectangular,parallelepiped and dried in a drying oven, and then calculated inaccordance with the following equation.

Porosity %=(apparent volume−true volume)/apparent volume×100  (1)

The “average pore diameter” is a value measured in accordance with ASTM(Designation: D4404-84) and is specifically a value determined by themeasurement of the diameter of pores in accordance with a mercurypenetration process using a mercury porosimeter manufactured by PorousMaterial, Inc.

A cleaning process using the sponge roller 1 will be describedhereafter.

As shown in FIG. 4, a rotating axis 7 is inserted into a hollow portionof a sponge roller 1 and a roll body 3 is fixed to the rotating axis 7.The cleaning of a material 9 to be cleaned is conducted by rotating therotating axis 7 so that a top portion 5 a of a protrusion 5 rotatinglycontacts the surface 9 a of the material 9. The top portion 5 a of theprotrusion 5 comprises the top end surface 13 b of the protruding endportion 13. As shown in FIG. 5, the top portion 5 a of the protrusionbrushes the surface 9 a by repeatedly pressing the protrusion 5 in alateral direction onto, and separating the protrusion 5 from, thematerial 9. A state in which the protrusion is pressed onto the material9 is called the deformed state, whereas a state in which the protrusion5 is separated from the material 9 is called the deformation releasedstate. In other words, the cleaning is conducted by repeating thedeformed state, each of the deformed states followed by the deformationreleased state.

When the sponge roller 1 undergoes a brushing motion, a tension actingon the protrusion 5 concentrates at a base end (a base end surface 11 aof a protruding 11). This is similar to the case shown in FIG. 6explained above, wherein the tension concentrated at the front end 55causes the protrusion 53 to be easily broken. However, as shown in FIG.5, the protruding base portion 11 according to the present embodimenthas the outer surface 15 formed divergently toward the periphery 3 a ofthe roll body 3. Thus, a sectional area of the protruding base portion11 is at its maximum at the base end surface 11 a and graduallydecreases toward the protruding end portion 13. Therefore, when theprotrusion 5 is pressed in a lateral direction, the stress concentrationin the vicinity of the base end surface 11 a is released. Accordingly,the tension is dispersed in the whole protruding base portion 11 and thedeformation and the resulting breakage in the vicinity of a front end 45in the transfer direction of the base end surface 11 a is securelyprevented. Accordingly, the durability of the protrusion 5 is increased.

Since the durability of the protrusion 5 can be improved by varying theprotruding base portion 11 and without by varying the protruding baseportion 11 and any influence on the shape of the protruding end portion13, the protruding end portion 13 to be contacted with the material 9 tobe cleaned can be freely set to the size and shape which are mostsuitable for brushing.

Hereinafter, a comparative tensile strength test will be described. Thetest concerns a comparison of a tensile strength of an objective sampleof the protrusion 5 of the sponge roller shown in FIG. 1(b) to acomparative sample of the protrusion 53 of the sponge roller shown inFIG. 6. For each of the objective sample and comparative sample, aPVAt-based porous material having a porosity of 90% and a compressionstress 30% in a proper water-containing state of 60 g/CM2 was used.

As for the protrusion 5 of the objective sample, a protrusion having thefollowing characteristics is used: a total height H being 4.5 mm, anouter diameter of the protruding end portion being 7.5 mm, a height h ofthe protruding base portion 11 being 1.5 mm, a crossed axes angle θ₁between the outer surface 3 a and inclined surface 15 being about 45°,and an outer diameter of the base end surface 11 a of the protrudingbase portion 11 being 10.5 mm. As for the protrusion 53 of thecomparative sample, a protrusion having the following characteristics isused: a total height being 4.5 mm and an outer diameter being 7.5 mm.

The procedure of the test will be described hereinafter. The protrusions5 and 53 are clamped by a clip (not shown) in a state where the rollbody 3 of each sample is retained between chucks (not shown) and theclip is stretched until the protrusions 5 and 53 are broken. At thatpoint, the tensile strength of each roller is measured.

The test results as shown in FIG. 8 reveal that the protrusion of thecomparative sample broke when the stretching load was increased to 1.59kg, whereas the protrusion of the objective sample did not break untilthe stretching load was 1.85 kg. Accordingly, the tensile strength ofthe objective sample is larger than that of the comparative sample by16.4%.

The second embodiment of the present invention will be described belowin reference to FIG. 7. FIG. 7 shows an enlarged sectional view of theprincipal portion, which shows a protrusion 63 of a PVAt-based cleaningsponge roller 61 according to the second embodiment. The protrusion 63according to the second embodiment differs from the protrusion 5according to the first embodiment in that the protruding base portion 65of the protrusion 63 has a curved outer surface 67 and that a curvedportion 59 is provided between the periphery 3 a of the roller body 3and the top end surface 13 b of the protruding end portion 13.

A crossed axes angle θ₂ between a straight line 75, which connects thebase end 71 and top end 73 of the outer surface 67 of the protrudingbase portion 65 shown in FIG. 7, and the periphery 3 a of the roll body3 in the cross section is set at approximately 30° to 60°.

In accordance with this embodiment, in the same manner as that in thefirst embodiment, not only can the durability of the protrusions 63 beimproved without adversely affecting the cleaning performance, but alsothe production cost can be reduced due to an improvement in yield.

With respect to the shape of the cross section of the protruding baseportions 11 and 65 and the protruding end portion 13, a generallycircular shape is used in the above explanation of the first and secondembodiments. However, according to the present invention, the shape isnot limited thereto and the cross section can take various shapes suchas rectangle, ellipse, oval, etc.

While the description above refers to particular embodiments of thepresent invention, it will be understood that many modifications may bemade without departing from the spirit thereof. The accompanying claimsare intended to cover such modifications as would fall within the truescope and spirit of the present invention.

The presently disclosed embodiments are therefore to be considered inall respects as illustrative and not restrictive, the scope of theinvention being indicated by the appended claims, rather than theforegoing description, and all changes which come within the meaning andrange of equivalency of the claims are therefore intended to be embracedtherein.

What is claimed is:
 1. A cleaning sponge roller made of a polyvinylacetal-based porous sponge having elasticity in a wet state, comprising:a generally cylindrical roll body defining a periphery; and a pluralityof protrusions integrally molded to the periphery of the roll body, eachof the protrusions having a tapered protruding base portion extendingfrom the periphery of the roll body, said base portion having a maximumsectional area at a base end thereof at the roll periphery and taperingto a top end thereof, and each protrusion further including a protrudingend portion extending from the top end of the respective base portion toa top portion of the protruding end portion with the end portion havinga generally uniform sectional shape such that the sectional area of theend portion is substantially uniform from adjacent the top end of thebase portion to the top portion of the protruding end portion and thesection area of the end portion is less than that of the base portion atthe base end thereof.
 2. The cleaning sponge roller according to claim1, wherein said protruding base portion has an outer surface formed in adivergent shape toward the periphery of the roll body.